5o INTERMEDIARY METABOLISM AND GROWTH I 



an exchange of glutainic-2-''*C with the glutamyl moiety of FGA (Miller and 

 Waelsch, 1956). A similar exchange reaction involving the intermediate in purine 

 degradation, formiminoglycine, and glycine-Q-'^^C is catalyzed by Clostridium 

 enzymes (Sagers ^^ a/., 1956). 



2) Formiminoglycine- '^C ^ THFA ^ ^ glycine-2-'''C + formimino THFA 



formate + NH, ^ THFA < ! H2O 



In E. coli, the amide nitrogen of glutamine is also an efficient precursor of 

 nitrogen one of the imidazole ring of histidine (Neidle and Waelsch, 1956). 



The second carbon of histidine is also a precursor of "active formate". Thus, 

 when histidine-2-^'*C is injected into rats, the label can be detected in the following 

 products of formate metabolism : a) the choline methyl groups of liver or hepatoma, 

 b) the methyl group of creatine, and c) urinary allantoin, and uric acid (Reid and 

 Landefeld, 1951; Reid et al., 1952). 



{b) Serine and glycine biosynthesis 



Interconversion of glycine and serine. A relationship between the amino acids, serine 

 and glycine, was demonstrated by Shemin. When serine labelled with ^^N in the 

 amino group and with ^^C in the carboxyl group was fed to rats, labelled glycine 

 could be isolated with no change in the ratio of ^^N to '-^C. This suggested that 

 the conversion of serine to glycine involved the splitting out of the beta carbon of 

 serine (Shemin, 1946). The reverse reaction, the formation of serine from glycine 



Serine + Pyridoxal phosphate -= — =- HOCH2— C — COOH 



N 



HCHO 



Glycine + Pynidoxal phosphate -^-^CHg—COOH 



Formomidino- 

 glutoric 



N'°-Formyl-tetra- 

 hydrofolic 



HCOOH 

 ATP 



Amino 

 imidazole carboxamide 



ribotlde 



Fig. 20. Role of pyridoxal phosphate and folic acid derivatives in serine and glycine 



interconversion. 



